poly IC
Meaning of poly IC: A stretch of synthetic double-stranded RNA carrying no message at all, built solely to look to the body like a virus.
Definition of poly IC
Poly IC is a synthetic double-stranded RNA made by pairing a chain of inosine with a chain of cytidine. Cells carry sensors that treat double-stranded RNA as proof of viral infection, so the molecule sets off an antiviral alarm with no virus present. It is used in the laboratory as a stand-in for infection and, in stabilized form, as a vaccine adjuvant.
Why does double-stranded RNA set off an alarm?
Because a human cell has almost no reason to contain any. The cell's own RNA is copied in single strands and used that way. Many viruses, by contrast, either carry a double-stranded genome or produce a double-stranded intermediate while copying themselves, so a long paired strand is close to a signature of infection. Sensors sit ready in two places to catch it: one inside the compartments where material swallowed from outside is inspected, and others floating loose in the cell interior. Poly IC satisfies those sensors while containing no viral gene and no instruction that could be read.
What does the cell do in response?
It releases interferon of the alpha and beta types, the family sent out early in a real infection. Neighboring cells receiving it shut down parts of their own machinery, making themselves poor hosts for a virus that has not arrived. Cells that present material to the immune system mature and become far better at it, natural killer cells are roused, and the response that follows leans toward killing infected cells rather than making antibody. That is exactly the profile wanted from a vaccine additive, which is why the compound is studied as an adjuvant and injected into tumors to make cold tissue look infected.
Why was the plain version replaced?
| Feature | Poly IC | Stabilized form |
|---|---|---|
| Make-up | Two paired synthetic RNA chains | The same chains with a polymer coat |
| Survival in blood | Cut apart within minutes | Resists breakdown far longer |
| Interferon response | Brief and unpredictable | Stronger and more sustained |
Enzymes in blood dismantle unprotected RNA quickly, so early trials of the bare molecule delivered fevers, chills and falling blood counts without a dependable effect. Coating it with a polymer and a cellulose derivative produced poly ICLC, the version now used in studies. A companion compound pairing adenosine with uridine, known as poly AU, works on the same principle.
Also known as
Used in a sentence
Poly IC was used to model a viral infection in the cultured cells.
Good to know
The characteristic response to poly IC is release of type I interferon, the alpha and beta forms, rather than interferon gamma, and the prefix poly here describes a repeating chain and is unrelated to the enzyme abbreviated PARP.